Carbon Incorporation during the Dielectric Breakdown Process of Silicon Oxide

Abstract

Modifications in the structure and composition of anodic silicon oxide film during the dielectric breakdown process have been studied by infrared spectroscopy (IR) and XPS. Before breakdown, the IR spectrum of the anodic silicon oxide film shows the band associated with the asymmetric stretching transverse mode of the SiO4 tetrahedra. However, after dielectric breakdown, apart from the strongest SiO band, carbon incorporation in the silicon oxide film is detected in the form of new bands as SiOC, CC, C=O and CH. Scanning electron microscopy observations show that the breakdown process is initiated in the form of islands consisting of pores and cracks randomly distributed across the otherwise flat surface of the silicon oxide. Energy-dispersive x-ray analysis in the damaged zones confirms the presence of carbon, which is attributed to the incorporation of carbon species from the organic electrolyte. After prolonged breakdown the cracks and pores cover the whole surface of the sample. In-depth XPS and IR analyses indicate that the breakdown areas have a layered structure. In all cases the inner layers, close to the substrate, are composed of silicon oxide, while the composition of the outer layers depends on the breakdown time: for short breakdown times a layer of SiOxCy material is formed, which is similar to a silicate rather than an oxycarbide structure. The Auger parameter of silicon obtained from XPS core-level and Auger electron energies is smaller than those of the oxides and carbides of silicon but coincides with those of silicates, suggesting also an open structure for the SiOxCy material. For long breakdown times an amorphous carbon outer layer is also detected. © 1997 by John Wiley & Sons, Ltd.